ES2795049T3 - Mesoporous silicas and their synthesis process - Google Patents

Abstract

A mesoporous silica prepared from components A and B, such that A is a surfactant of the saponin family and B is a precursor of silica, said silica comprises between 1% and 30% by weight of surfactant.

Description

DESCRIPTION

Mesoporous silicas and their synthesis process

Field of the invention

The present invention relates to a mesoporous silica and to a method for producing said silica. The process and silica are characterized by the use of natural compounds that belong to the saponin family as a structuring agent.

State of the art

Thanks to their high specific surface area, porous materials and in particular mesoporous silicas are of great interest in fields as varied as catalysis, electronics, semiconductors, composite materials, and are currently also an irreplaceable tool in the biological and medical fields. .

The mechanism of synthesis of organized mesoporous siliceous materials is well known. This mechanism, called CTM (Cooperative Templating Mechanism or cooperative assembly mechanism), suggests that the addition of a silica precursor leads, by interaction with the aggregates formed by a surfactant, to the formation of an organized organic / inorganic hybrid phase. Therefore, this mechanism is based on a self-assembly between the surfactant molecules and the inorganic precursor that leads to an organization of the system. There is a wide range of surfactants that can be used as structuring agents in mesoporous silica synthesis processes. They can be anionic, cationic or neutral.

Whatever the synthesis processes used, the surfactants are, in all cases, of non-natural origin. These are petroleum-based molecules that must be extracted from the final material to, on the one hand, allow further use in medical, biological or pharmaceutical applications and, on the other hand, to release the porosity. EP 2256088 uses a calcination process to extract surfactant molecules. This process, in addition to consuming energy, destroys the used surfactant which, if it is expensive, cannot enter a recycling process. Calcination also has the drawback of modifying the physicochemical properties of mesoporous materials. This process decreases, for example, the mesh parameter (Bérubé and Kaliaguine. Micropor Mesopor Mat. 2008, 115: 469-479). On the other hand, the exothermic nature of the process increases the defects present in the inorganic structure.

There are other techniques for extracting the surfactant from the mesoporous material. We can cite an extraction process by sulfuric acid described by Zhuang, Quian and Wan in Applied Surface Science, 2010, 256; 5343-5348 "An alternative method to remove PEO-PPO-PEO template in organic-inorganic mesoporous nanocomposites by sulfuric acid extraction". This process has the disadvantage of altering the surfactant that it can no longer be recycled. In addition, this technique requires the installation of an expensive and heavy acid recycling system.

The works by Tanev and Pinnavaia (Mater. 1996, 8 (8): 2068-2079) describe a process for solvent extraction of surfactant. Extraction is facilitated when the surfactant is nonionic. Although this process has the advantage of allowing recycling of the surfactant, its removal from the porous material remains incomplete. Therefore, this process is generally combined with calcination that allows to completely release the porosity of the synthesized material.

Finally, Huang, Xu and Li (Separation and Purification Technology, 118; 120-126 "Effect of the polar modifiers on supercritical extraction efficiency for template removal from hexagonal mesoporous silica materials: solubility parameter and polarity considerations") show that a supercritical fluid can allow the surfactant to be extracted from the mesoporous material. If this process effectively removes the surfactant and keeps it intact, its implementation on an industrial level is complicated.

Therefore, the mesoporous silicas of the prior art must be subjected to a process that allows the removal of the surfactant. This process is quite complicated, energy consuming and expensive. Therefore, a need exists for a process for the synthesis of mesoporous silica and a mesoporous silica in which removal of the surfactant can be avoided and / or facilitated and / or inexpensive.

The present invention aims to provide a solution to at least one of the problems mentioned above. The invention provides a process for the synthesis of mesoporous silica and a mesoporous silica obtained by the process. The process and the silica are as described in the claims.

Presentation of the invention

In a first aspect, the present invention provides a mesoporous silica prepared by mixing components A and B such that A is a surfactant of the saponin family and B is a precursor of silica.

The silica precursor is represented by the formula Si (ORi) (OR ² ) (OR ³ XOR ⁴ ) where Ri, R ² , R ³ and R ⁴ are independently chosen from hydroxyl groups, alkyls, glycols, trimethyl-1, 2,3,4-tetrahydronaphthalene, 1,1,1,3,3,3-hexafluoropropan-2-yl, dimethylsilyl, trimethylsilyl, ethoxysilyl, tributoxysilyl, diethoxy (methoxy) silyl, trimethoxysilyl, ethoxy (dimethoxy) silyl, butoxy ( dipropoxy) silyl, tripropoxysilyl, diethoxy (trimethylsilyloxy) silyl, ethoxy-bis (trimethylsilyloxy) silyl, methyl-bis (trimethylsilyloxy) silyl, butoxy-bis (trimethylsilyloxy) silyl, diethoxy (triethoxysilyloxy, vinyl) silyl, dimethylsilyloxy (trimethylsilyloxy) (3-methylpentoxy) silyl, 4,7,7-trimethyl-3-bicyclo [2.2.1] heptanyl, 2,2,4-trimethyl-3-bicyclo [2.2.1] heptanyl, propan-2-yloxy-bis (trimethylsilyloxy) silyl, dibutoxy (trimethylsilyloxy) silyl, trimethyl trimethoxysilyl, dibutoxy (ethenyl) silyl, diethyl bis (trimethylsilyl), (butan-2-yloxy) silyl, diacethyloxy - [(2-methylpropan-2-yl) oxy] , acetyloxy (diethoxy) sil yl, 4- (dimethylamino) phenyl, 4- (dimethylamino) phenyl, 2- (diethylamino) ethyl, pyridin-3-yl, 2-methylpropan-2-yl) oxy, 2,2,3,3,4,4 , 5,5,6,6,7,7-dodecafluoroheptyl, trichloro-2-ethylbutoxy, cyclononyl, 1-methoxypropan-2-yl, 2- (2-methoxyethoxy) ethyl, 2-butoxyethyl, 2-ethoxyethyl, 2- methoxyethyl, acetyl, acetyloxy (dipropoxy) silyl, 5-methyl-2-propan-2-ylcyclohexyl, butan-2-yloxy, methylphenyl, cyclohexyl, 2-aminoethyl, phenyl, prop-2-enyl, 2-fluoroethyl, acetate or trihydroxysilyloxy. The configuration R1 = R2 = R3 = R4 is covered by the invention, or by the formula xSiO ² : MyO where M is one or more metal atoms, one or more transition metal atoms, one or more non-metallic atoms, a methylammonium, an actinide, y = 1 or 2 or 3 or 4 and x is the SiO ² / MyO molar ratio.

In a second aspect, the present invention provides a method for producing mesoporous silica in which components A and B are mixed in a solvent comprising water, such that A is a surfactant of the saponin family and B is a precursor. silica represented by the formula Si (OR ¹ ) (O2) (O3) (O4) where R ¹ , R ² , R ³ and R ⁴ are independently chosen from the groups hydroxyl, alkyls, glycols, trimethyl-1,2, 3,4-tetrahydronaphthalene, 1,1,1,3,3,3-hexafluoropropan-2-yl, dimethylsilyl, trimethylsilyl, ethoxysilyl, tributoxysilyl, diethoxy (methoxy) silyl, trimethoxysilyl, ethoxy (dimethoxy) silyl, butoxy (dipropoxy) silyl, tripropoxysilyl, diethoxy (trimethylsilyloxy) silyl, ethoxybis (trimethylsilyloxy) silyl, methyl-bis (trimethylsilyloxy) silyl, butoxy-bis (trimethylsilyloxy) silyl, diethoxy (triethoxysilyloxy) silyl, dimethyl (trimethylsilyloxy) silyl, dimethyl (trimethylsilyloxy) silyl ) silyl, 4,7,7-trimethyl-3-bicyclo [2.2.1] heptanyl, 2,2,4-trimethyl-3-bicyclo [2.2.1] heptanyl, propan-2- yloxy-bis (trimethylsilyloxy) silyl, dibutoxy (trimethylsilyloxy) silyl, trimethyl trimethoxysilyl, dibutoxy (ethenyl) silyl, diethyl bis (trimethylsilyl), (butan-2-yloxy) silyl, diacetyloxy - [(2-methylpropan-2-yl) oxy] silyl, acetyloxy (diethoxy) silyl, 4- (dimethylamino) phenyl, 4- (dimethylamino) phenyl, 2- (diethylamino) ethyl, pyridin-3-yl, 2-methylpropan-2-yl) oxy, 2,2 , 3,3,4,4,5,5,6,6,7,7-dodecafluoroheptyl, trichloro-2-ethylbutoxy, cyclononyl, 1-methoxypropan-2-yl, 2- (2-methoxyethoxy) ethyl, 2- butoxyethyl, 2-ethoxyethyl, 2-methoxyethyl, acetyl, acetyloxy (dipropoxy) silyl, 5-methyl-2-propan-2-ylcyclohexyl, butan-2-yloxy, methylphenyl, cyclohexyl, 2-aminoethyl, phenyl, prop-2- enyl, 2-fluoroethyl, acetate, trihydroxysilyloxy. The configuration R1 = R2 = R3 = R4 is covered by the invention,

or

by the formula xSiO ² : MyO where M is one or more metal atoms, one or more transition metal atoms, one or more non-metallic atoms, a methylammonium, an actinide, y = 1 or 2 or 3 or 4 and x is the SiO ² / MyO molar ratio.

The mesoporous silica of the invention can be used in the fields of human or animal nutrition, of human or animal nutrition, of the pharmaceutical industry, of the cosmetic industry.

The method and silica of the invention have several advantages over prior art silicas and their production methods. The method of the invention makes it possible to produce a silica comprising a natural and food-grade surfactant, in particular, a surfactant belonging to the saponin family. Silica comprising the natural surfactant can be used for various applications. The total removal of the surfactant is not necessarily necessary and its presence at the silica level has no negative effect in the various applications envisaged for silica.

The fact that the silica can be used without the total removal of the surfactant allows (i) to maintain the properties of the silica and avoid any alteration of the silica that may be caused by the treatments, in particular by calcination, aimed at the removal of the surfactant; (ii) considerably reduce the time and / or cost of preparing the silica; and (iii) preserve the environment by avoiding the use of chemicals or energy-consuming methods to remove the surfactant.

Maintaining the properties of silica (point (i) above) makes it possible to guarantee the efficiency and optimization of the applications that use the silica of the invention.

In the event that surfactant has to be removed, the inventive method and silica remain advantageous compared to prior art silicas and methods. Indeed, the process and the silica of the invention allow the removal of the surfactant by a simple washing with water or with a hydroalcoholic solution. Using a food grade surfactant allows for residual surfactant presence. When using more toxic surfactants, it becomes necessary to remove all traces of surfactants, especially for food, medical or even cosmetic applications, and then it is often necessary to carry out a high temperature calcination step, which is not the case in the present invention.

Brief description of the figures

Figure 1 shows a photograph taken by a Philips XL 30 ESEM electron microscope depicting silica particles.

Figure 2 is a graph showing the liquid nitrogen adsorption isotherm at 77 K for particles obtained in Example 1.

Figure 3 shows a photograph representing silica particles obtained in Example 2. The photograph was taken by a Philips XL 30 ESEM electron microscope.

Figure 4 is a graph showing the liquid nitrogen adsorption isotherm at 77 K for particles obtained in Example 2.

Figure 5 shows a photograph representing silica particles obtained in Example 3 taken with a Philips XL 30 ESEM electron microscope.

Figure 6 shows a photograph representing silica particles obtained in Example 3 and, in particular, the porosity of the particles obtained made by the Philips XL 30 ESEM electron microscope.

Figure 7 is a graph showing the liquid nitrogen adsorption isotherm at 77 K for particles obtained in Example 3.

Figure 8 is a photograph representing silica particles obtained in Example 5 taken by a Philips XL 30 ESEM electron microscope.

Figure 9 is a graph showing the liquid nitrogen adsorption isotherm at 77 K for particles obtained in Example 4.

Description of the invention

The present invention relates to a method for the production of mesoporous silica. The method is characterized by the use of at least one natural and food-grade compound, in particular, from the saponin family as a structuring agent. The method can be a sol-gel or spray-drying synthesis. The invention also relates to mesoporous silica obtained by said process.

Unless otherwise indicated, all terms used in the disclosure of the invention, including technical and scientific terms, have the meanings generally understood by those skilled in the art. Definitions of terms are included to better appreciate the teaching of the present invention.

As used herein, the following terms have the following meanings:

"A", "an" and "the", as used herein, refer to referents in both the singular and plural unless the context clearly indicates otherwise. By way of example, "a compartment" refers to one or more than one compartment.

"Approximately" as used herein, refers to a measurable value such as a parameter, an amount, a time duration, and so on, means to include variations of / - 20% or less, preferably / - 10% or less, more preferably / - 5% or less, even more preferably / - 1% or less and always more preferably / - 0.1% or less and compared to the specified value, provided that such variations are suitable to function in the described invention . However, it will be understood that the value referred to by the modifier "about" is also specifically disclosed.

"Comprising", "comprising" and "comprises" and "composed of" as used herein are synonyms for "include", "including", "includes" or "contain", "containing", "contains" and are inclusive or open terms that specify the presence of the following, for example, a component and do not exclude or rule out the presence of components, particularities, elements, organs, stages, supplementary, not cited, known in the art or disclosed in the itself.

The citation of the numerical ranges by limits includes all the numbers and fractions included in this range, as well as the cited limits.

The mesoporous silica of the invention is also designated by the terms green silica or green silica.

The terms "structuring agent" and "surfactant" are used synonymously.

In a first aspect, the present invention provides a mesoporous silica prepared from components A and B such that A is a surfactant of the saponin family and B is a precursor of silica. Silica is obtained by mixing components A and B. The precursor can be soluble or insoluble in water.

In a preferred embodiment, the silica precursor is represented by the formula Si (OR ¹ ) (OR2) (OR3) (OR4) where Ri, R ² , R ³ and R ⁴ are independently chosen from the groups hydroxyl, alkyls, glycols, trimethyl-1,2,3,4-tetrahydronaphthalene, 1,1,1, 3,3,3-hexafluoropropan-2-yl, dimethylsilyl, trimethylsilyl, ethoxysilyl, tributoxysilyl, diethoxy (methoxy) silyl, trimethoxysilyl, ethoxy (dimethoxy) silyl, butoxy (dipropoxy) silyl, tripropoxysilyl, diethoxy (trimethylsilyl, diethoxy) silyl bis (trimethylsilyloxy) silyl, methyl-bis (trimethylsilyloxy) silyl, butoxy-bis (trimethylsilyloxy) silyl, diethoxy (triethoxysilyloxy) silyl, dimethyl (vinyl) silyl, trimethylsilyloxy, (3-methylpentoxy) silyl, 4,7,7-trimethyl -3-bicyclo [2.2.1] heptanyl, 2,2,4-trimethyl-3-bicyclo [2.2.1] heptanyl, propan-2-yloxy-bis (trimethylsilyloxy) silyl, dibutoxy (trimethylsilyloxy) silyl, trimethyl trimethoxysilyl, dibutoxy (ethenyl) silyl, diethyl bis (trimethylsilyl), (butan-2-yloxy) silyl, diacetyloxy - [(2-methylpropan-2-yl) oxy] silyl, acetyloxy (diethoxy) silyl, 4- (dimethylamino) phenyl, 4- (dimethylamino) phenyl, 2- (diethylamino) e tyl, pyridin-3-yl, 2-methylpropan-2-yl) oxy, 2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptyl, trichloro-2-ethylbutoxy, Cyclononyl, 1-methoxypropan-2-yl, 2- (2-methoxyethoxy) ethyl, 2-butoxyethyl, 2-ethoxyethyl, 2-methoxyethyl, acetyl, acetyloxy (dipropoxy) silyl, 5-methyl-2-propan-2-ylcyclohexyl , butan-2-yloxy, methylphenyl, cyclohexyl, 2-aminoethyl, phenyl, prop-2-enyl, 2-fluoroethyl, acetate or trihydroxysilyloxy. The configuration R1 = R2 = R3 = R4 is covered by the invention.

The alkyl groups are preferably chosen from methyl and ethyl groups. It is preferable that all O-R bonds are hydrolyzable. The preferred silica precursor of formula Si (OR) 4 is tetraethyl orthosilicate and / or tetramethyl orthosilicate.

According to an embodiment of the invention, the silica precursor is represented by the formula xSiO ² : MyO where M is one or more metal atoms, one or more transition metal atoms, one or more non-metallic atoms, a methylammonium , an actinide, y = 1 or 2 or 3 or 4 and x is the SiO ² / MyO molar ratio. The metal atom can be alkaline at (y = 2) or alkaline earth (y = 1). The silica precursor of the formula xSiO ² : MyO can be selected from the group comprising orthosilicate, sodium, potassium or calcium metasilicate.

In a preferred embodiment, the structuring agent belongs to the saponin family. Saponins are amphiphilic molecules naturally produced by certain plants or animals and which have surfactant properties. The most important sources of saponins used in the food and cosmetic industry are the Quillaja saponaria Molina tree, Yucca schidigera and the Southeast Asian shrub Camellia sinensis, known as the "tea plant ".

The inventors have discovered that the cooperative self-assembly mechanism can be carried out in the presence of natural surfactants of the saponin type. It appears that, as in the case of "classical" industrial surfactants, the saponins aggregate to form, with the silica precursor, a hybrid phase in which the synthesis of mesoporous material will occur.

The saponins used in the context of this invention are triterpenoid glycosides whose main structure (I) aglycone (sapogenin) can take the following forms: dammarenediols (dammarans), cucurbitadienol (cucurbitans), hopanol (hopanes), lanosterols (lanostans), thyrucalladienol ( tirucallanos), p-amyrin (oleans), ~ -amyrin (ursanos), taraxasterols (taraxasterans), lupeol (lupanes).

Methyl radicals, carboxylic, aldehyde or alcohol functions; hydrogen atoms, hydroxyl groups; as well as simple or branched glycosidic chains are also attached to the aglycone backbone. Within the glycosidic chains, the following sugars are preferred: D-glucose, L-rhamnose, D-galactose, D-glucuronic acid, L-arabinose, D-xylose, D-fructose, D-adipose, D-fucose. In the case that the aglycone comprises a glycosidic chain, it will speak of monodesmoside and, in the case that two glycosidic chains are attached to the aglycone skeleton, it will speak of bidesmoside.

In a preferred embodiment, the saponin used has the following oleanane structure such that R1 and R4 are methyl groups, R2 is a hydrogen atom and R3 is a carboxylic group.

Structure (I)

According to another advantageous embodiment, the structuring agent contains one or more of the following saponins: saponin 1, saponin 2, saponin 3, saponin 4, saponin 5, saponin 6, saponin 7, saponin 8, saponin 9, saponin 10, Saponin 19, Saponin 20a, Saponin 20b, Saponin 21a, Saponin 21b, Saponin 22a, Saponin 22b, Saponin 23, Saponin S7, Saponin S8, Saponin S9, Saponin S10, Saponin S11, Saponin S12, Quillaja Saponins 7, 17, 1821 ( also known as ^q A-7, QA-17, ^q A-18, QA-21).

According to one embodiment of the invention, the saponins used have a steroidal aglycone backbone of the spirostanol or furostanol type or a steroidal glycoalkaloid structure of the spirosolane or solanidane type.

In a preferred embodiment, the mesoporous silica of the invention comprises a maximum of 30% by weight of structuring agent with respect to the weight of the solid, preferably between 1 and 20% and more advantageously between

1 and 5% by weight of structuring agent with respect to the solid. Said weight of the solid refers to the sum of the weight of the silica and the structuring agent.

In a preferred embodiment, the silica comprises mesopores whose minimum average diameter is 1 nm. The diameter of the pores was calculated from the nitrogen sorption isotherms at liquid nitrogen temperature

(77 K) according to the method of Barrett, Joyner and Halenda (BJH). The diameter of the silica mesopores, established from the nitrogen sorption isotherm at 77 K, is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19,

20, 21, 22, 23, 24 or 25 nm or any value between the above values.

In a preferred embodiment, the specific surface area of silica, calculated from nitrogen sorption isotherms at liquid nitrogen temperature (77 K) by the Brunauer, Emmett and Teller theory (BET), is at least 20 m2 / g, 40 m2 / g, 50 m2 / g, or 60 m2 / g. The specific surface is a maximum of 80 1000 m2 / g or 1500 m2 / g or any value between the above values.

In a preferred embodiment, the pore volume of the silica was calculated from the nitrogen sorption isotherms at liquid nitrogen temperature (77 K) by the method of Barrett, Joyner and Halenda (BJH). Said pore volume is at least 0.1 cm3 / g, 0.2 cm3 / g, 0.4 cm3 / g, 0.5 cm3 / g and at most 0.6 cm3 / g, 0.8 cm3 / g , 1 cm3 / g, 1.2 cm3 / g, 1.5 cm3 / g or any value between the above values.

In a second aspect, the present invention provides a method for producing mesoporous silica in which components A and B are mixed in a solvent comprising water, such that A is a natural surfactant of the saponin family and B is a silica precursor. Components A and B are as described above. The production method is carried out from a micellar solution of surfactant in a solvent comprising water to which the silica source is added. Said source of silica is preferably added dropwise. Preferably, the solvent is water or a hydroalcoholic solution. The surfactant is as described above.

In a preferred embodiment, the silica precursor is represented by the formula Si (OR) 4 where R is an alkyl group, or by the formula xSiO ² : MyO where M is a metal atom, y = 1 or 2 and x is the SiO ² / MyO molar ratio. The silica precursor is as described above.

In a preferred embodiment, the surfactant is added to the solvent in an amount sufficient to obtain a micellar concentration between 0.1 and 1000 times the critical micellar concentration. Preferably, the surfactant is added to the solvent in an amount sufficient to obtain a micellar concentration of between 10 and

900 times, 20 and 800 times, 30 and 700 times, 40 and 600 times, 50 and 500 times, 60 and 400 times, 70 and 300 times, 80 and

200 times, 90 and 100 times the critical micellar concentration or all values between the above values.

In a preferred embodiment, the silica precursor is added to the solvent in an amount sufficient so that the ratio between the amount of silica precursor and the amount of structuring agent is between 0.1 and 50. The silica precursor it is preferably added dropwise to the solvent.

In a preferred embodiment, the temperature of the solution obtained after adding the silica precursor to the solvent is kept between 15 and 35 ° C, preferably between 20 and 25 ° C. The pH of the surfactant solution is at a maximum of 7. The solution can have an acidic pH which is obtained by adding suitable solutions and / or molecules such as HCl. The pH of the solvent can be 0, 1, 2, 3, 4, 5, 6, 7 or any value between the above values. The pH of the solvent is preferably 1.

In a preferred embodiment, the mixture is left to settle for at least 5 hours and at most 24 hours at a minimum temperature of 20 ° C, the rest is followed by a filtration step that allows obtaining a solid product a. The mixture can also be stirred for at least 10 minutes at a minimum temperature of 20 ° C, stirring is followed by evaporation of the mixture, thus obtaining a solid product b. The product a and / or the product b is then subjected to at least one wash with an ethanol solution, water or a hydroalcoholic solution at atmospheric pressure. The washed product is then subjected to at least one drying step under reduced pressure of 0.1 to 20 mm Hg.

In a preferred embodiment, the production method of mesoporous silica comprises the following steps:

- the introduction of saponins in acidified water in an amount necessary and sufficient to obtain a micellar concentration comprised between 0.1 and 1000, preferably between 1 and 1000 times the CMC;

- dissolving the saponins by keeping the solution at a temperature between 15 and 35 ° C;

- the dropwise addition of a silica precursor so that the ratio between the amount of silica precursor and the amount of structuring agent is between 0.5 and 50, preferably between 1 and 50;

- aging of the mixture without stirring for a period of time ranging from 10 to 100 hours and preferably from 10 to 20 hours at a temperature between 20 and 70 ° C;

- filtration of the aged product in Büchner;

- Carrying out successive washes at atmospheric pressure and at a controlled temperature with a 40% vol ethanol solution; and

- drying the product under reduced pressure.

In a preferred embodiment, the production method of mesoporous silica comprises the following steps:

- The introduction of saponins in acidified water or not in a volume necessary and sufficient to obtain a micellar concentration of between 0.1 and 1000, preferably between 1 and 1000 times the CMC;

- The dissolution of the saponins keeping the solution at a temperature between 15 and 35 ° C;

- The dropwise addition of a silica precursor so that the ratio between the amount of silica precursor and the amount of structuring agent is between 0.5 and 50, preferably between 1 and 50;

- The aging of the mixture with or without stirring, for 30 minutes to 72 hours at a temperature between 20 and 30 ° C;

- The implementation of evaporation by means of aerosol. The precursor-surfactant mixture is drawn into the spray dryer and pushed through a two-fluid or ultrasonic nozzle having a 0.15 to 1.2 mm orifice to generate drops of about 20 pm. The temperature at the inlet of the column is between 120 and 250 ° C and preferably between 140 and 180 ° C. An air flow with a power of less than 1 m3 / min and a suitable temperature in the upper part of the column allows, 1) the evaporation of the aqueous solvent, 2) the self-assembly of the surfactant micelles and 3) the condensation of the precursor silica.

- The off-white powder obtained is washed as previously described.

The method of the invention makes it possible to obtain high yield rates of the order of 60 to 90% with respect to the expected mass in solid. Said mass refers to the sum of the mass of the silica and the structuring agent.

The mesoporous silica synthesis process according to the invention is characterized by mixing and reacting a silica precursor and a natural structuring agent. The invention is also characterized by the fact that, taking into account the chemical and biological properties of the structuring agent, its removal becomes optional. Advantageously, the structuring agent is not removed, which makes it possible to accelerate the industrial process and reduce the cost of industrialization.

In the event that the elimination of the structuring agent and, therefore, of the saponin is foreseen or required, this can be eliminated by washing with subcritical water or by successive washing with water or with a 40% water / ethanol mixture vol without necessarily having to use a calcination stage. The extracted saponin could be used for the production of other mesoporous silicas and / or for other applications known to those skilled in the art.

Examples

Example 1:

12 N hydrochloric acid is added to 115 ml of water so that the pH is between 1 and 2. An amount of saponin (ABCR) that allows to obtain 10 times the critical micellar concentration is dissolved with stirring at 25 ° C in this volume of acidified water. Next, an amount of tetraethoxysilane is added which makes it possible to obtain a precursor / structure agent ratio of 50 with stirring dropwise at a rate of 0.3 grams per minute. The mixture obtained has a pH between 1 and 2. The mixture is aged without stirring for 16 hours at 65 ° C. The gel obtained is filtered on Büchner, washed several times with a 40% vol ethanol solution before being dried under reduced pressure at 40 ° C. The powder obtained is white. The recovered "green" mesoporous silica has a specific surface area determined by the BET method of 850 m2g-1, a pore volume of 0.7 cm3g_1 and mesopores of 35 A. The shape of the particles obtained includes spheres and blocks of silica ( Figure 1 taken by the PHILIPS XL 30 ESEM electron microscope).

Comparative example 2:

1.5 g of the mesoporous silica obtained according to example 1 were calcined at 500 ° C for 4 hours. The powder obtained is white. Mesoporous silica has a specific surface area of 750 m2g-1, a pore volume of 0.6 cm3g_1 and mesopores of 32 A.

Example 3:

A quantity of saponin (Q-Naturale 200- Desert King) having a triterpenic saponin content of 67 to 73% (dry weight) is dissolved with stirring at 25 ° C in a volume of acidified water that allows to obtain a concentration corresponding to 10 times the critical micellar concentration. Then, an amount of tetraethoxysilane is added which makes it possible to obtain a precursor / structure agent ratio of 10 with dropwise stirring at a rate of 0.3 grams per minute. The mixture obtained has a pH between 1 and 2. The mixture is aged without stirring for 12 to 16 hours at room temperature. The sol thus obtained is introduced into an atomizer (spray dryer) (ProCept R&D spray dryer - Belgium) and sprayed using a two-fluid nozzle having a 0.4 mm orifice under a compressed air pressure of 6 bar. . The quantity of solution to be sprayed is 200 ml. The operating conditions of the spray dryer are as follows:

- The incoming air temperature is fixed at 180 ° C

- The temperature at the outlet of the column is 60 ° C

- The atomization speed is 7L.min-1

2.24 grams of white mesoporous silica powder with a very low bulk density are collected.

The powder obtained is observed by electron microscopy and the analysis shows the presence of cup-shaped particles that are characteristic of spray drying syntheses (Waldron K et al. Formation of monodisperse mesoporous silica microparticles via spray drying. Journal of Colloid and Interface Science 418 (2014) 225-233). The synthesized material has a specific surface area of 648 m2g-1, a pore volume of 0.38 cm3 g-1 and mesopores of 3.2 nm. Figure 5, recorded from an ESEM PHILIPS XL 30 electron microscope, shows the shape of the particles obtained. An image showing porosity is shown in Figure 6 recorded from a PHILIPS XL 30 ESEM electron microscope.

Example 4:

A quantity of saponin (Q-Naturale 200- Desert King) having a triterpenic saponin content of 67 to 73% (dry weight) is dissolved with stirring at 25 ° C in a volume of acidified water that allows to obtain a concentration corresponding to 10 times the critical micellar concentration. Then, an amount of potassium metasilicate is added which makes it possible to obtain a precursor / structure agent ratio of 10 with stirring dropwise at a rate of 0.3 grams per minute. The mixture obtained has a pH between 1 and 2. The mixture is aged without stirring for 12 to 16 hours at room temperature. The sol thus obtained is introduced into an atomizer (spray dryer) (ProCept R&D spray dryer - Belgium) and sprayed using a two-fluid nozzle having a 0.4 mm orifice under a compressed air pressure of 6 bar. . The quantity of solution to be sprayed is 200 ml. The operating conditions of the spray dryer are as follows:

- The incoming air temperature is fixed at 180 ° C

- The temperature at the outlet of the column is 60 ° C

- The atomization speed is 7L.m¡m1

- 3.19 g of white mesoporous silica powder are collected, which has a very low apparent density.

The white powder obtained is washed with water and then observed by electron microscopy in a Philips microscope. XL30 ESEM. The analysis shows the presence of spherical particles, as well as particles of less well defined shape.

The synthesized material has a specific surface of 50 m2g-1, a pore volume of 0.23 cm3g-1 and mesopores of 19 nm.

Claims (15)

1. A mesoporous silica prepared from components A and B, such that A is a surfactant of the saponin family and B is a precursor of silica, said silica comprises between 1% and 30% by weight of surfactant. 2. The mesoporous silica according to claim 1, in which the mesopores have a minimum size of 1 nm, calculated from the nitrogen sorption isotherms at liquid nitrogen temperature (77 K) according to the method of Barrett, Joyner and Halenda (BJH). 3. The mesoporous silica according to claim 1 or 2, the pore volume of which is at least 0.1 cm3 / g, calculated from nitrogen sorption isotherms at liquid nitrogen temperature (77 K) according to the method of Barrett, Joyner and Halenda (BJH). The mesoporous silica according to one of claims 1 to 3, wherein the surfactant is food grade. 5. Method for producing mesoporous silica, in which components A and B are mixed in a solvent comprising water, such that A is a surfactant of the saponin family and B is a precursor of silica. 6. Method according to claim 5, wherein the silica precursor is represented by the formula Si (OR ¹ ) (OR ² ) (OR ³ ) (OR ⁴ ) where R ¹ , R ² , R ³ and R ⁴ are independently selected from the groups alkyl, hydroxyl, glycols, trimethyl-1,2,3,4-tetrahydronaphthalene, 1,1,1,3,3,3-hexafluoropropan-2-yl, dimethylsilyl, trimethylsilyl, ethoxysilyl, tributoxysilyl, diethoxy (methoxy) silyl, trimethoxysilyl, ethoxy (dimethoxy) silyl, butoxy (dipropoxy) silyl, tripropoxysilyl, diethoxy (trimethylsilyloxy) silyl, ethoxy-bis (trimethylsilyloxy) silyl, methyl-bis (trimethylsilyloxy) silyl (trimeoxylsilyl-bis (trimethylsilyloxy) silyl) , diethoxy (triethoxysilyloxy) silyl, dimethyl (vinyl) silyl, trimethylsilyloxy, (3-methylpentoxy) silyl, 4,7,7-trimethyl-3-bicyclo [2.2.1] heptanyl, 2,2,4-trimethyl-3- bicyclo [2.2.1] heptanyl, propan-2-yloxy-bis (trimethylsilyloxy) silyl, dibutoxy (trimethylsilyloxy) silyl, trimethyl trimethoxysilyl, dibutoxy (ethenyl) silyl, diethyl bis (trimethylsilyl), (butan-2-yloxy) silyl, diacetyloxy - [(2-methylpropan-2-yl) oxy] silyl, acetyloxy (diethoxy) silyl, 4- (dimethylamino) phenyl, 4- (dimethylamino) phenyl, 2- (diethylamino) ethyl, pyridin-3-yl, 2- methylpropan-2-yl) oxy, 2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptyl, trichloro-2-ethylbutoxy, cyclononyl, 1-methoxypropan-2-yl, 2- (2-methoxyethoxy) ethyl, 2-butoxyethyl, 2-ethoxyethyl, 2-methoxyethyl, acetyl, acetyloxy (dipropoxy) silyl, 5-methyl-2-propan-2-ylcyclohexyl, butan-2-yloxy, methylphenyl, cyclohexyl , 2-aminoethyl, phenyl, prop-2-enyl, 2-fluoroethyl, acetate or trihydroxysilyloxy or by the formula xSiO ² : MyO where M is one or more metal atoms, one or more transition metal atoms, one or more non-metallic atoms, a methylammonium, an actinide, y = 1 or 2 or 3 or 4 and x is the SiO ² / MyO molar ratio. 7. Method according to claim 5 and / or 6, in which the surfactant is added to the solvent in an amount sufficient to obtain a micellar concentration between 1 and 1000 times the critical micellar concentration. Method according to one of claims 5 to 7, in which the silica precursor is added to the solvent in an amount sufficient so that the ratio between the amount of silica precursor and the amount of surfactant is between 0.5 and fifty. Method according to one of claims 5 to 8, in which the temperature of the solvent is kept between 15 and 35 ° C. 10. Method according to one of claims 5 to 9, wherein the pH of the solvent is at most 7. Method according to one of claims 5 to 10, in which the mixture is left to stand for at least 5 hours at a minimum temperature of 20 ° C, followed by a filtration step to stand, thus obtaining a solid product a. Method according to one of claims 5 to 11, in which the mixture is stirred for at least 10 minutes at a minimum temperature of 20 ° C, The stirring is followed by evaporation and / or aspiration of the mixture, thus obtaining a solid product b. Method according to claim 11 and / or 12, in which product a and / or product b is subjected to at least one washing with an ethanol solution at atmospheric pressure. Method according to claim 13, wherein the washed product is subjected to at least one pressure drying step. 15. Use of mesoporous silica as described in claims 1 to 4 for uses in the fields of cosmetics or human or animal nutrition.